1. Field of the Invention
The present invention relates to a cleaning device for use in an electrophotographic image forming apparatus such as a copying apparatus or a laser beam printer. The present invention alsao relates to an electrophotographic process cartridge incorporating such a cleaning device and an image forming apparatus which detachably incorporates such a process cartridge.
2. Description of the Related Art
FIG. 11 illustrates a known cleaning device which is used for the purpose of removing residual toner and other foreign matter remaining on an image carrier in an electrophotographic image forming apparatus.
In the operation of the electrophotographic image forming apparatus, a toner image corresponding to image information is formed on a cylindrical photosensitive member (referred to as "photosensitive drum", hereinafter) which serves as the image carrier, through an image forming process having sequential steps such as charging, exposure, and development. The toner image thus formed is transferred from the surface of the photosensitive drum 1 to a transfer member such as a paper sheet through an image transferring step.
In this image transferring step, part of the toner on the photosensitive drum 1 remains without being transferred to the transfer member. Such toner remaining on the photosensitive drum will be referred to as "residual toner". Such residual toner and other foreign matter is removed by a cleaning device 6.
The cleaning device 6 has a resilient cleaning blade 60, a receiving sheet (referred to also as an "anti-blowing member") 6a for preventing blowing out of the toner, and a cleaning vessel 6b which supports the cleaning blade 60 and the receiving sheet 6a. The cleaning blade 60 has a tabular supporting metal sheet 61 and a rubber tip member 62. A predetermined level of pressure is applied to two portions of the cleaning blade 60 so that the edge portion 62a of the rubber tip member 62 is pressed at a suitable level of pressure onto the surface of the photosensitive member 1.
As the photosensitive drum 1 rotates in the direction of the arrow R1, the residual toner on the photosensitive drum 1 is brought to the region where the rubber tip member 62 contacts the surface of the photosensitive drum 1, so that the residual toner is scraped off the photosensitive drum surface by the edge of the rubber tip member 62 so as to be collected in the cleaning vessel 6b. The receiving sheet 6a is disposed upstream of the cleaning blade 60 as viewed in the direction of rotation of the photosensitive drum 1 and is held in contact with the surface of the photosensitive drum 1, thus preventing the removed toner from falling or being blown off in a downward direction.
As the number of the image transfer cycles increases due to repeated production and transfer of images, residual toner and other foreign matter is gradually accumulated in the region where the rubber tip member 62 of the cleaning blade 60 contacts the surface of the photosensitive drum 1, i.e., in the vicinity of the edge 62a. The foreign matter, in addition to the residual toner, include, for example, dust generated due to grinding of the photosensitive surface of the photosensitive drum 1. The toner and other foreign matter thus accumulated serve as a "lubricant". Thus, a lubricating effect cannot be obtained while the accumulation of the toner and other foreign matter is still small, i.e., at the beginning of the use of the cleaning device 6. Consequently, there is a considerably high level of friction between the photosensitive drum 1 and the cleaning blade 60 when the use of the cleaning device 6 has just started, leading to problems or troubles such as a increase in the level of the torque required for driving the photosensitive drum 1, generation of noise and, in some cases, roll-up or turn-over of the rubber tip member 62 of the cleaning blade 60 downstream as viewed in the direction of rotation of the photosensitive drum 1.
In order to eliminate these problems, hitherto, it has been a common practice to apply a lubricant L to the edge 62a of the rubber tip member 62 of the cleaning blade 6 before the cleaning blade is put to use, thus reducing the friction acting between the photosensitive drum 1 and the cleaning blade 60 in the break-in period of the cleaning device 6.
Lubricants conventionally used are sorted according to shape into two types: namely, a spherical particle-type lubricant and an indefinite-form, particle-type lubricant. These two types of lubricants have their own problems when put to use.
The spherical, particle-type lubricant provides a superior lubrication effect due to the sphericity of the particles, but tends to be separated from the edge 62a of the cleaning blade 60. It is therefore often experienced that the lubricant of this type comes off the edge portion due to vibration of the edge portion 62a. For instance, when a contact-type charging member is used for the purpose of electrostatically charging the photosensitive drum 1, the portions of the drum surface around the regions contacted by both end portions of the contact-type charging member tend to be roughened due to extraordinary discharge, resulting in a local increase in the friction coefficient at these portions of the drum surface. When the edge 62a of the cleaning blade 60 contacts these roughened portions, the edge 62a minutely vibrates to release the lubricant. The portion of the edge 62a devoid of the lubricant exhibits rapid wear of the material of the tip member and, in the worst case, triggers the aforesaid turn-over of the cleaning blade. One of effective measure for eliminating such a problem is to increase the amount of the spherical-particle type lubricant initially applied to the edge 62a so as to maintain the lubricant on the edge 62a for a longer time. Increasing of the amount of lubricant applied causes the amount of the lubricant coming off the edge 62a to be increased correspondingly. The freed lubricant existing on the photosensitive drum 1 tends to impair the image exposure so as to promote degradation of the quality of product images.
The lubricant of the second-mentioned type, i.e. the, indefinite-form, particle-type lubricant, exhibits a greater adhesion to the edge 62a than the spherical, particle-type lubricant, so that the lubrication effect lasts for a relatively long time, thus obviating the above-described problem encountered with the use of spherical, particle-type lubricant. The indefinite-form, particle-type lubricant, however, exhibits a lubricating effect which though long-lasting is smaller than that exhibited by the spherical, particle-type lubricant. When this type of lubricant is used, therefore, noise tends to be generated due to vibratory action of the cleaning blade 60 on the photosensitive drum 1, in the initial period of use of the cleaning device before the lubrication effect produced by accumulated toner and other matter grows to a sufficiently high level, particularly when the friction between the cleaning blade 60 and the photosensitive drum 3 is increased due to softening of the cleaning blade 60, which takes place when the temperature is elevated. In order to overcome this problem, hitherto, it has been necessary to lower the friction coefficient of the surface of the photosensitive drum 1 or to reduce the pressure of contact of the cleaning blade 60 within a range, which does not substantially impair the cleaning performance.
The use of either the spherical particle-type lubricant or the indefinite-form, particle-type lubricant alone poses various restrictions in the design in regard to the condition of application of the lubricant, the condition of contact of the resilient cleaning blade, coefficient of friction of the photosensitive drum 1 and so forth, in order that all the requirements are met by the single type of lubricant.